The present invention relates to the field of uniform illumination systems, and more particularly to systems and methods for providing uniform illumination using integrator lenslet arrays, for example in image projection devices.
It is well known to employ integrator lenslet arrays to provide a high intensity, uniform illumination, for example for image projection systems. In general, a high intensity lamp is provided, typically with a paraboloid reflector, directing illumination generally along a single axis. This light varies in spatial intensity depending on position with respect to the lamp, so a pair of spaced integrator plates, each composed of a corresponding array of lenslets, is provided. The light passing through each respective set of lenslets is then directed toward the image plane, through an optical relay lens system. Thus, the integrator plates serve to image the lamp from various vantage points, which are then summed, resulting in a uniform illumination.
One problem arising from this construction is that a proportion of the light exiting from the lamp, including both direct and reflected rays, is not collimated, and is thus directed at stray angles. This, in turn, causes so-called side lobes, in which light entering one lenslet of the first integrator plate is refracted toward a non-corresponding lenslet of the second integrator plate. This, in turn, results in rays which either do not strike the imaging plane or are directed at steep angles. In either case, this stray light can adversely affect the performance of the system. In particular, stray light created by these side lobes can scatter from various objects in the optical path, compromising the contrast of the system. These lenslet arrays are becoming very popular method of producing a uniform image from the lamp and, as their size decreases, the intensity of the side lobes also increases.
Thus, there is a need for an light integrator system which provides uniform and efficient illumination while eliminating sidelobe illumination.
JP 11-1160791 A relates to an illumination optical device for a projection display device. The system includes a lamp with a concave reflector, a pair of integrator lenslet arrays spaced by a light guide, and a relays lens system. In this system, light guides are provided to guide light from the lenslet of the first lens array plate to the lenslet of the second lens array plate for reduced light loss and increased efficiency. Thus, off axis rays are apparently guided to the second lenslet array, rather than absorbed.
EP 0 773 456 A2 provides a magnifying lens and display apparatus in which lens pairs may be held in relative position by a tubular structure. The axes of the sets of lens pairs are generally convergent, and the tubular structure formed of a black pigmented resin. The structure is thus employed as a compound magnifying lens for human visualization.
The present invention provides, according to one embodiment, a set of baffles, for example conduits or sheets, with light absorptive walls between respective lenslets or arrays of lenslets of the integrator plates, to interrupt propagation of the sidelobe rays.
These sidelobe-suppressed light integrator subsystems are especially useful in image projection systems, wherein stray light reduces contrast and may result in artifacts and poor image quality. The light integrator subsystem is, for example, inserted between the lamp and imaging panel.
It is noted that, while a portion of the light is lost in the conduit or baffle array, this light is considered parasitic on creation, and therefore its loss is not considered to substantially decrease efficiency of the system. Thus, by eliminating or decreasing these parasitic rays, performance is improved by ensuring high image contrast and fewer artifacts.
The conduit or baffle array is preferably non-reflective, since conserving these rays by reflection does not correct their propagation axis, and thus these rays would still exit from the integrator system at an undesired angle creating unwanted scatter light.
According to a preferred embodiment, the imaging device is rectangular, and therefore the integrator optics are designed to produce a uniform rectangular illumination at the focal plane thereof. In such a system, wherein the lenslets are disposed in a rectangular array with unequal horizontal and vertical spacing, the quantitative effect of sidelobe rays is anisotrophic such that the intensity of the side lobes being much stronger in smaller dimension of the lenslets. Thus, as shown in FIG. 3, the Y-axis lobes have greater intensity than the X-axis lobes. Thus, the problem may be addressed asymmetrically. Thus, for example, a set of parallel sheets may be provided between successive rows of lenslets along the Y-axis. While this does not substantially alter the X-axis sidelobe intensity, the Y-axis sidelobes will be substantially attenuated. By providing sheets instead of conduits or tubes, heat dissipation is enhanced, construction simplified, and light loss reduced, with some residual stray light.
In the case of conduits or tubes, sidelobes along both axes are suppressed. The array is preferably composed of rectangular tubular structures. In order to provide spatial efficiency, the walls of adjacent integrator structures are preferably common. The walls are preferably coated with a non-reflective black coating, to absorb light incident thereon. Between the lenslet array and conduit array, an air space may be provided for passive or forced convection. The external portion of the conduit array may be provided with a surface area for convective or radiant cooling. The conduit is preferably formed of a heat-tolerant thermally conductive material, such as copper or aluminum, although other materials may be suitable.
Therefore, it is an object of the invention to provide a lenslet integrator system having a pair of spaced integrator lenslet arrays, characterized in that a conduit is disposed between respective lenslet elements of the integrator to absorb stray light.
It is also an object of the invention to provide a conduit array for a lenslet integrator system, having a set of rectangular apertures corresponding to the lenslet array configuration and a non-reflective surface.
It is a further object of the invention to provide an optical illumination apparatus, comprising an illumination source; a first array of lenslets disposed along an illumination path of said illumination source; a conduit array, having a respective aperture corresponding to a plurality of said lenslets of said first array of lenslets, said conduit array having non-reflective optically absorptive walls; a second array of lenslets, aligned with said conduit array such that rays, passing through a respective one of said first array of lenslets and not intercepting said non-reflective optically absorptive walls, intersect a respective one of said second array of lenslets; and a relay optical structure for integrating light emitted from said second array of lenslets on a focal plane.
These and other object will be apparent from a review of the drawings and detailed description of the preferred embodiment.